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  • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
  • C01G23/0536—Producing by wet processes, e.g. hydrolysing titanium salts by hydrolysing chloride-containing salts
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  • H01M4/00—Electrodes
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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention is an ultrafine particle dioxide suitable as a photocatalyst, a solar cell material, a lithium ion battery electrode material raw material such as lithium titanate (Li 4 Ti 5 O 12 ), and a dielectric raw material such as barium titanate (BaTiO 3 ).
• the present invention relates to titanium, a method for producing the same, a composition containing the ultrafine titanium dioxide, a solar cell material, a lithium ion battery electrode material, and a dielectric material.
• Titanium dioxide has a very wide range of industrial applications, such as cosmetics, UV shielding materials, and additives for silicone rubber.
• photocatalysts, solar cell materials, lithium ion battery electrode materials, dielectric materials, etc. Is a wide variety.
• Ultrafine titanium dioxide has attracted attention as an electrode material for lithium ion batteries and a high-performance dielectric material.
• the range of the primary particle diameter of ultrafine titanium dioxide is not clearly defined.
• the term “ultrafine particle” is used for fine particles of about 100 nm or less, but the ultrafine particle titanium dioxide of the present invention has an average primary particle diameter (D) converted from a BET specific surface area as described later.
• BET is titanium dioxide with a thickness of 2 to 20 nm.
• Li 4 Ti 5 O 12 which is a typical negative electrode material for lithium ion batteries, is generally obtained by a solid phase reaction between a lithium raw material and titanium dioxide. Specifically, it is manufactured by a step of uniformly mixing a lithium raw material and titanium dioxide, a step of drying the mixture, and a step of heat treatment. In this mixing step, titanium oxide is mixed in a liquid in which a lithium raw material is dispersed in water, and lithium hydroxide, lithium oxide, lithium carbonate, or the like can be used as the lithium raw material.
• titanium dioxide anatase type and hydrous titanium oxide having better reactivity than rutile type are preferred.
• Titanium dioxide has attracted attention as a high-performance dielectric material, and is used as a material for BaTiO 3 , for example.
• This BaTiO 3 is used as a constituent material of the dielectric layer of the multilayer ceramic capacitor.
• BaTiO 3 is obtained by the following reaction under heating. BaCO 3 + TiO 2 ⁇ BaTiO 3 + CO 2
• the above reaction is a solid phase reaction, and it is said that BaCO 3 is decomposed and BaO is generated at a high temperature, and BaO diffuses and dissolves in TiO 2 particles to become BaTiO 3 . Therefore, the size of the BaTiO 3 particles is affected by the size of the raw material TiO 2 particles.
• Titanium dioxide is applied to various uses as described above, but it is important that it has good dispersibility in order to bring out its function. For example, in the solid phase reaction of the lithium raw material and titanium dioxide, the reactivity and quality variations are determined by the mixed state of both. For this reason, titanium dioxide with low aggregation and high dispersibility is required. Titanium dioxide with low dispersibility requires a step of breaking up aggregation, which requires excessive energy for crushing, and may cause problems such as contamination of wear and unevenness of particle size. Also, high dispersibility is required when using titanium dioxide as a photocatalyst. If the dispersibility is poor, the concealing power becomes strong, so that the applications that can be used are limited.
• titanium dioxide having poor dispersibility is difficult to transmit light, and therefore, titanium dioxide that can contribute to light absorption is limited, and thus photoelectric conversion efficiency is deteriorated.
• titanium dioxide when titanium dioxide is used as an electrode material or a dielectric material for a lithium ion battery, the primary particle size is small, and it has excellent affinity with other materials used for an electrode material or a dielectric material for a lithium ion battery. There is a need for ultrafine titanium dioxide.
• titanium dioxide is roughly divided into a gas phase method in which titanium tetrachloride is reacted with an oxidizing gas such as oxygen or water vapor, and a liquid phase method in which titanium tetrachloride or titanyl sulfate is hydrolyzed in a solution.
• an oxidizing gas such as oxygen or water vapor
• titanium tetrachloride or titanyl sulfate is hydrolyzed in a solution.
• Titanium dioxide powder with high crystallinity and excellent dispersibility can be obtained by the vapor phase method, but since it is reacted at a high temperature exceeding 500 ° C., grain growth and sintering between particles proceed, and the dioxide dioxide having a high specific surface area. It is difficult to obtain titanium efficiently (Patent Document 1).
• titanium dioxide produced by the liquid phase method is produced at a temperature of about 300 ° C. even at a high temperature from room temperature, grain growth is suppressed and ultrafine titanium dioxide is easily obtained.
• silica, alumina, or an organic compound is modified on the titanium dioxide surface as a dispersant for the purpose of maintaining the dispersibility of the slurry for a long period of time. Examples have been reported.
• the liquid phase method using these dispersants may not be suitable depending on the intended use because a dispersant that becomes an impurity is added to titanium dioxide.
• a dispersant that becomes an impurity is added to titanium dioxide.
• titanium dioxide when titanium dioxide is used as a dielectric raw material, a solar cell material application, or a photocatalyst application, if a corrosive component such as chlorine is present, the substrate is corroded or deteriorated. The chlorine content needs to be kept low.
• impurities such as iron (Fe), aluminum (Al), silicon (Si), and sulfur (S) must be avoided as much as possible to adversely affect their electrical characteristics.
• titanium dioxide causes coloring, so titanium dioxide containing Fe is not suitable for use in applications requiring transparency, and Al, S Titanium dioxide containing a large amount of components causes lattice defects and degrades the performance of the photocatalyst.
• Patent Document 2 describes a method for producing ultrafine titanium dioxide obtained by hydrolyzing titanium tetrachloride in water and then separating and drying the product.
• Patent Document 2 is a method for obtaining brookite-type titanium dioxide, and the specific surface area measured by the BET method is as low as 200 m 2 / g or less, and thus the average primary particle size is large.
• An object of the present invention is to provide ultrafine titanium dioxide having a small average primary particle diameter (D BET ) and a large amount of moisture adsorption, a method for producing the same, a composition containing the ultrafine titanium dioxide, a solar cell material, lithium An electrode material raw material and a dielectric raw material for an ion battery are provided.
• D BET small average primary particle diameter
• the present inventors have made various studies to obtain ultrafine titanium dioxide having high dispersibility without modifying the surface of titanium dioxide with a dispersant such as silica.
• a dispersant such as silica.
• water vapor was measured by adding sulfuric acid and having a fine average primary particle diameter (D BET ), measured at 25 ° C. and relative humidity 90% (RH). It has been found that ultrafine titanium dioxide having a large amount of adsorption (water adsorption amount) can be obtained.
• the ultrafine particle titanium dioxide of the present invention has a small average primary particle diameter (D BET ).
• the ultrafine titanium dioxide of the present invention since the ultrafine titanium dioxide of the present invention has a large amount of moisture adsorption, it is considered to have high hydrophilicity and excellent dispersibility when dispersed in water. Furthermore, since the ultrafine titanium dioxide of the present invention has a large amount of moisture adsorption, when used as an electrode material for lithium ion batteries or a raw material for dielectrics, other raw materials such as lithium salt compounds, barium salt compounds, etc. This metal salt compound is considered to have higher affinity than conventional ultrafine titanium dioxide.
• the present invention is as shown in the following (1) to (14).
• Ultrafine titanium dioxide comprising a reaction step in which titanium tetrachloride is hydrolyzed in water, and a sulfuric acid addition step in which sulfuric acid is added after the reaction conversion rate of titanium tetrachloride reaches 80% or more and less than 100%. Manufacturing method.
• the ratio of sulfuric acid to the total amount of titanium tetrachloride and sulfuric acid [H 2 SO 4 / (H 2 SO 4 + TiCl 4 )] (mol%) is 4 mol% to 33 mol% (1) Or the manufacturing method of the ultrafine particle titanium dioxide as described in (2).
• a dechlorination (Cl) step of separating titanium dioxide and hydrochloric acid generated by the hydrolysis reaction using one or more of an ultrafiltration membrane, a reverse osmosis membrane, an ion exchange resin, and an electrodialysis membrane ( 1) The method for producing ultrafine titanium dioxide according to any one of (5). (7) The method for producing ultrafine titanium dioxide according to any one of (1) to (6), which comprises a drying step of drying ultrafine titanium dioxide.
• the average primary particle diameter (D BET ) calculated from the BET specific surface area is 2 to 20 nm, the water adsorption amount measured at 25 ° C. and relative humidity 90% (RH) is 16 to 35% by mass Fine particle titanium dioxide.
• (11) A composition containing the ultrafine particle titanium dioxide according to any one of (8) to (10) or the ultrafine particle titanium dioxide obtained by any one of the methods (1) to (7).
• (12) A material for a solar cell containing the ultrafine particle titanium dioxide according to any one of (8) to (10) or the ultrafine particle titanium dioxide obtained by any one of the methods (1) to (7).
• ultrafine titanium dioxide having a small average primary particle size and a large amount of moisture adsorption compared to conventional titanium dioxide, a method for producing the same, a composition containing the ultrafine titanium dioxide, and a solar cell Materials, lithium ion battery electrode material and dielectric material are provided.
• Titanium dioxide according to the present invention is suitable for photocatalyst applications, solar cell material applications, lithium ion battery electrode material applications, dielectric material applications, etc., and does not require special crushing treatments or dispersants. It is a great value.
• the ultrafine titanium dioxide of the present invention has an average primary particle diameter (D BET ) of 2 to 20 nm as converted from the BET specific surface area, and has a water adsorption amount of 16 measured at 25 ° C. and a relative humidity of 90% (RH). It is an ultrafine particle titanium dioxide of ⁇ 35% by mass.
• the ultrafine particle titanium dioxide of the present invention has an average primary particle diameter (D BET ) of 2 to 20 nm converted from the BET specific surface area calculated by the method shown in the Examples described later, preferably It is 2 to 18 nm, more preferably 3 to 15 nm, still more preferably 3 to 7.5 nm, and still more preferably 3 to 6 nm. If D BET is less than 2 nm, the cohesive property becomes strong and cannot be dispersed, which is inconvenient in handling, and if it exceeds 20 nm, the performance of the original ultrafine titanium dioxide cannot be sufficiently exhibited.
• D BET average primary particle diameter
• the ultrafine particle titanium dioxide of the present invention has a moisture adsorption amount of 16 to 35% by mass, preferably 18 to 32% by mass, measured at 25 ° C. and a relative humidity of 90% (RH), which will be described later.
• the content is preferably 19 to 30% by mass. If it is less than 16% by mass, the effect of improving the dispersibility and affinity of titanium dioxide may not be obtained. When the amount exceeds 35% by mass, moisture absorption and desorption are increased, so that management of the weight is necessary and handling properties are inferior.
• the ultrafine particle titanium dioxide of the present invention has a higher amount of moisture adsorption than conventional ultrafine particle titanium dioxide and has a higher affinity for moisture. Therefore, the ultrafine particle titanium dioxide of the present invention is excellent in affinity with a metal salt compound which is contained in a dielectric material, an electrode material for a lithium ion battery or the like and is a material having a high affinity for moisture. It is thought that there is.
• the ultrafine particle titanium dioxide of the present invention has a BET specific surface area of 75 to 750 m 2 / g, preferably 83 to 750 m 2 / g, measured by the method shown in the examples described later. It is preferably 100 to 500 m 2 / g, more preferably 200 to 500 m 2 / g, still more preferably 250 to 500 m 2 / g.
• the titanium dioxide of the present invention preferably contains an anatase crystal structure suitable as a dielectric material or an electrode material material for a lithium ion battery as a main component.
• the anatase content measured by the method shown in the Examples described later is more preferably 90% or more, further preferably 95% or more, and still more preferably 100%.
• An anatase content of 90% or more is preferable because the reaction to a complex oxide such as a dielectric material proceeds efficiently.
• the titanium dioxide of the present invention has a chlorine (Cl) and sulfur (S) content of preferably 0.1% by mass or less, more preferably 0.08% by mass or less, and still more preferably 0.0. 05% by mass or less.
• Cl chlorine
• S sulfur
• the content of each element of carbon (C), aluminum (Al), silicon (Si), and iron (Fe) is preferably less than 0.01% by mass, and more preferably 0.005% by mass. And more preferably less than 0.001% by mass.
• 0.0001 mass% or more is preferable from a cost viewpoint of a manufacturing method.
• titanium dioxide when used as a raw material for barium titanate, it is necessary to strictly control the mixing ratio of the barium source and titanium dioxide at the time of synthesizing the dielectric raw material. If there are few impurities to be generated, the composition of the obtained barium titanate is less likely to be shifted. Moreover, if these impurities are small, not only can the deviation of the mixing ratio be reduced, but a raw material having excellent dielectric properties can be obtained.
• the method for producing ultrafine titanium dioxide of the present invention comprises a reaction step of hydrolyzing titanium tetrachloride in water, and sulfuric acid to which sulfuric acid is added after the reaction conversion rate of titanium tetrachloride becomes 80% or more and less than 100%. It is a manufacturing method including an addition process.
• ultrafine titanium dioxide having a high specific surface area and moisture adsorption can be obtained by controlling the reaction temperature and the reaction conversion rate within a specific range in the reaction step.
• the method of the present invention separates the ultrafine titanium dioxide from the titanium dioxide slurry, a cooling step for cooling the reaction solution after addition of sulfuric acid, a dechlorination (Cl) step for removing hydrochloric acid, and a titanium dioxide slurry. It is preferable to include at least one of a step of performing and a step of drying the separated ultrafine particle titanium dioxide.
• titanium tetrachloride is hydrolyzed in water.
• titanium hydroxide is produced.
• titanium hydroxide is polycondensed, titanium dioxide nuclei are generated, and the nuclei grow into primary particles.
• the main crystal forms produced here are anatase and rutile, but anatase is produced at the beginning of the reaction, and the action of hydrochloric acid changes the anatase to rutile, which is a stable phase.
• titanium tetrachloride and water may be mixed and subjected to a hydrolysis reaction.
• a titanium tetrachloride aqueous solution is prepared, and the titanium tetrachloride aqueous solution and water are mixed and subjected to a hydrolysis reaction.
• a hydrolysis reaction Is preferred.
• titanium tetrachloride or titanium tetrachloride aqueous solution and water can be mixed more uniformly.
• the reaction is preferably performed at a temperature of 45 to 75 ° C, more preferably at a temperature of 50 to 75 ° C. Is reacted at a temperature of 50-70 ° C. If it is 45 degreeC or more, reaction will progress at a practical speed, and if it is 75 degreeC or less, it can suppress that reaction progresses too rapidly and the effect of the sulfuric acid added at a sulfuric acid addition process is exhibited.
• the concentration of titanium (Ti) contained in the titanium tetrachloride aqueous solution to be used is preferably 5 to 25% by mass, more preferably 10 to 20%. % By mass, more preferably 15 to 20% by mass. If the titanium (Ti) concentration is 5% by mass or more, titanium hydroxide is difficult to precipitate at room temperature, which is preferable for storage. If it is 25% by mass or less, aggregated particles are less likely to be generated, which is preferable for storage.
• the titanium (Ti) concentration in the reaction mixture obtained by mixing the aqueous titanium tetrachloride solution with water is preferably 0.05 to 10% by mass, more preferably 1 to 5% by mass, and still more preferably 1 to The amount is 3% by mass, and more preferably 1 to 2% by mass. If the Ti concentration is 0.05% by mass or more, the productivity is high, and if the Ti concentration is 10% by mass or less, a decrease in yield due to a decrease in reactivity due to an increase in Ti concentration can be suppressed.
• a method for producing titanium dioxide by hydrolysis of titanium tetrachloride a method is used in which water and titanium tetrachloride or an aqueous solution of titanium tetrachloride are mixed and then the mixture is preferably heated from room temperature to be hydrolyzed. .
• titanium tetrachloride has a uniform concentration distribution, nucleation occurs uniformly.
• hydrolysis depends on the heating rate and the heating temperature, the reaction rate proceeds relatively slowly.
• the temperature of the aqueous titanium tetrachloride solution before the temperature rise is not particularly limited, but is preferably 40 ° C. or lower, more preferably 30 ° C. or lower, still more preferably 25 ° C.
• the rate of temperature rise is preferably 0.1 to 0.8 ° C./min, more preferably 0.2 to 0.7 ° C./min, still more preferably 0.3 to 0.6 ° C./min, and more More preferably, it is 0.35 to 0.45 ° C./min. If the heating rate is 0.1 ° C / min or more, the reaction proceeds at a practical reaction rate, so that productivity can be secured and the heating rate is slower than 0.8 ° C / min. If so, nucleation is more dominant than particle growth, and particles of 200 m 2 / g or more may be easily obtained.
• the stirring device used for mixing may be a rotary blade stirrer that is generally used widely, and the shape of the rotary blade may be a general one such as a propeller shape, a turbine shape, or a comb shape. Two or more stirrers may be attached inside or a baffle may be installed. Also, not limited to batch reactors, continuous tank reactors or tube reactors in which the reaction tank is a continuous tank and titanium tetrachloride and water are continuously charged while the reaction solution is taken out on the opposite side of the inlet. Can also be used.
• the reaction conversion rate of titanium tetrachloride is 80% or more, more preferably 85% or more, still more preferably 90% or more, still more preferably 95% or more, and still more preferably 97% or more. Sometimes an aqueous sulfuric acid solution is added. When the reaction conversion rate of titanium tetrachloride is less than 80%, the reaction does not proceed sufficiently, and the effect of sulfuric acid added in the sulfuric acid addition step is not sufficiently exhibited.
• the sulfuric acid addition step it is preferable to add sulfuric acid at a temperature of 45 to 75 ° C. If it is 45 ° C. or higher, titanium tetrachloride is sufficiently hydrolyzed, and if it is 75 ° C. or lower, temperature control when the sulfuric acid solution is added can be easily performed. From this viewpoint, the temperature is preferably 50 to 75 ° C, more preferably 60 to 75 ° C, and still more preferably 65 to 75 ° C.
• the sulfuric acid concentration in the sulfuric acid aqueous solution added in the sulfuric acid addition step is preferably 40 to 80% by mass, more preferably 45 to 65% by mass, still more preferably 45 to 60% by mass, and still more preferably 45 to 55% by mass. is there.
• the concentration of 40% by mass or more can be adjusted so that the temperature range of the reaction solution does not deviate from 45 to 75 ° C. when added to the reaction solution described above. Moreover, if it is a density
• the sulfuric acid aqueous solution to be added may be prepared by mixing commercially available concentrated sulfuric acid and water, or commercially available diluted sulfuric acid may be used, and the method is not particularly limited.
• the ratio of sulfuric acid to the total amount of titanium tetrachloride and sulfuric acid [H 2 SO 4 / (H 2 SO 4 + TiCl 4 )] (mol%) is preferably 4 to 33 mol%. If it is 33 mol% or less, it is preferable because sulfuric acid can be easily removed, an increase in the SO 4 component as an impurity can be reduced, and the intended use is not limited. Moreover, if it is 4 mol% or more, the effect of a sulfuric acid will be easy to express. From this viewpoint, the amount of the sulfuric acid is more preferably 8 to 33 mol%, further preferably 16 to 33 mol%, and still more preferably 20 to 28 mol%.
• the reaction solution after the addition of sulfuric acid is preferably cooled to 60 ° C. or less in order to obtain high titanium dioxide having an anatase content of 90% or more.
• the cooling process also contributes to the generation of rutile crystals, and the shorter the time that the reaction solution is maintained at 60 ° C. or higher, the more the crystal form can be prevented from changing from anatase crystals to rutile crystals, and the anatase content is reduced. improves.
• rutile crystals have a more hydrophobic particle surface than anatase crystals, rutile particles tend to aggregate, and dispersibility decreases.
• the cooling method is not limited.
• the use of heat exchangers, or liquids such as cold water and liquid nitrogen may be directly charged into the reactor, and solids such as ice and dry ice are charged, and a method of cooling by blowing a gas such as N 2 or air. Can be adopted.
• the dechlorination (Cl) process of the present invention is for removing hydrochloric acid generated by hydrolysis of titanium tetrachloride and added sulfate ions.
• a method of separating hydrochloric acid a method of substituting with pure water using an ultrafiltration membrane or a reverse osmosis membrane, or a method of deionizing using an electrodialysis membrane or an ion exchange resin may be used. The combined method is preferable. By these methods, in addition to chlorine ions, other anions such as sulfate ions can be removed.
• This dechlorination step is preferably performed after the cooling step or after the sulfuric acid addition step, and more preferably after the cooling step.
• composition, material for solar cell, electrode material for lithium ion battery and dielectric material contains the ultrafine titanium dioxide described above.
• the solar cell material, the lithium ion battery electrode material, and the dielectric material of the present invention each contain the aforementioned ultrafine titanium dioxide. That is, the ultrafine titanium dioxide of the present invention has a small average primary particle diameter (D BET ) and a large moisture adsorption amount, and is therefore suitable as a material for solar cells, a material for electrode materials for lithium ion batteries, and a dielectric material. .
• D BET small average primary particle diameter
• D BET Average primary particle size
• X-ray diffraction measurement is performed on the powder obtained by drying titanium dioxide, and the peak height (abbreviated as Ha) corresponding to the anatase type crystal, the peak height (abbreviated as Hb) corresponding to the brookite type crystal, and the rutile type.
• the peak height (abbreviated as Hr) corresponding to the crystal was calculated by the following formula (3).
• Anatase content (%) [Ha / (Ha + Hb + Hr)] ⁇ 100 (3)
• X-ray diffraction measurement was performed under the conditions of a sampling width of 0.0167 deg and a scanning speed of 0.0192 deg / s.
• Chlorine (Cl) A solution obtained by adding a hydrofluoric acid aqueous solution to titanium dioxide and heating and dissolving it with a microwave was measured by potentiometric titration with silver nitrate.
• Sulfur (S) Measured by high frequency induction furnace combustion / infrared absorption method.
• Carbon (C) Measured by high frequency induction furnace combustion / infrared absorption method.
• Iron (Fe) Measured by atomic absorption method.
• Aluminum (Al) and silicon (Si) Measured by fluorescent X-ray analysis (XRF).
• Example 1 690 mL of ion-exchanged water was charged into a reaction tank equipped with a comb stirrer. The mixture was stirred at about 300 rpm, and 50 g of a titanium tetrachloride aqueous solution (Ti concentration: 18% by mass) at room temperature (20 ° C.) was added dropwise thereto and stirred and mixed in the reaction vessel. After adding the titanium tetrachloride aqueous solution, the temperature was raised at a rate of temperature rise of 0.4 ° C./min to 70 ° C. Sampling at that time and measuring the reaction conversion rate was 95%. The reaction time was as shown in Table 1.
• Example 2 The temperature increase rate after the addition of titanium tetrachloride was 0.2 ° C./min, the temperature was increased until it reached 55 ° C., and the sulfuric acid was added when the reaction conversion rate was 92%. Titanium dioxide was obtained. The measurement results are shown in Table 1.
• Example 3 The temperature increase rate after adding titanium tetrachloride was 0.1 ° C./min, the temperature was increased until it reached 45 ° C., and the sulfuric acid was added when the reaction conversion rate was 90%. Titanium dioxide was obtained. The measurement results are shown in Table 1.
• Comparative Example 1 The temperature increase rate after the addition of titanium tetrachloride was 0.1 ° C./min, the temperature was increased until it reached 40 ° C., and in the same manner as in Example 1 except that sulfuric acid was added when the reaction conversion rate was 75%, Titanium dioxide was obtained. The measurement results are shown in Table 1.
• Comparative Example 2 The temperature increase rate after adding titanium tetrachloride was 0.4 ° C./min, and the temperature was increased until it reached 80 ° C. The reaction conversion rate at this time was 97%. Thereafter, titanium dioxide was obtained in the same manner as in Example 1 except that sulfuric acid was not added. The measurement results are shown in Table 1.
• Comparative Example 3 690 mL of ion-exchanged water was charged into a reaction tank equipped with a comb stirrer and heated to 95 ° C. While stirring at about 300 rpm, while maintaining the temperature at 95 ° C., 50 g of a titanium tetrachloride aqueous solution (Ti concentration: 18% by mass) at room temperature (20 ° C.) was added dropwise over 30 seconds, and stirred and mixed in the reaction vessel. Maintained for a minute. Then, without adding sulfuric acid, the reaction vessel was cooled to 50 ° C. in less than 1 minute in an ice bath (cooled to 60 ° C. over 40 seconds). Other than that was carried out similarly to Example 1, and obtained titanium dioxide. The measurement results are shown in Table 1.
• the ultrafine titanium dioxide of the present invention has a small average primary particle diameter (D BET ) and a large amount of moisture adsorption, so the hydrophilicity of the particle surface is high.
• D BET small average primary particle diameter
• materials for solar cells, dielectric materials, lithium ions It is considered to be excellent in affinity with the auxiliary material mixed with the battery electrode material and the like, and is ultrafine titanium dioxide having extremely useful characteristics.

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